Arcade Switching Power Supply Repair - SBL1640PT?

[acebh]

I have a switching power supply that the original owner said +5v is missing.  Apparently sent for some students at a tech school to look at and they said it was the 5v voltage regulator?  Which I found interesting considering these don't use voltage regulator ICs  .  The fuse is NOT blown.

I tested the SBL1640PT +5v (schottky barrier rectifier / output diodes) out of circuit using the diode setting on my multimeter.  It reads .155v on each diode one way, and infinite the other way on both.  Should the reading be closer to .5v to .7v out of circuit like most other diodes?  I also tested the 12v and 5v diodes and they read around .3v with diode test in-circuit.

[MonMotha]

Schottkys tend to have quite a bit lower forward voltage than typical "silicon diodes".  They're used in many low-voltage SMPS designs because they're fast, and the lower voltage drop drastically increases efficiency.

These things are so cheap they're not usually worth troubleshooting.  You can usually replace them entirely for $20-50 or even less for a used part.

If you do want to troubleshoot, a better description of what's happening would be useful.  Do you have every voltage except 5V, or do you have no outputs at all?

[acebh]

I figured the schottky's might register lower.. just didn't know if .155v was low enough to indicate a bad component.  Figured if anyone had one in their parts bin they could measure with diode test or anyone had experience with what would be considered a "good" reading then that might help.

I could pick another power supply for $20-30 or less on eBay but I like fixing this stuff when I can =)  Actually I have a spare one that blew a fuse and just needed a bridge rectifier replaced and is now working great.. but I'd like to fix this one too.  You know, the whole "throw away society" mentality.  For $2-3 I should be able to fix it 'good as almost new'

[boardjunkie]

It shouldn't be all that difficult to repair a switcher if you want to. Just be careful with them if t-shooting while power'd up. If you use a scope, power it via an isolation transformer to get it off the line or else you'll melt the probe down and possibly damage the scope.

Most likely suspects are filter caps and regulator transistors/diode packs related to the voltage rail that is missing. If all voltages are missing, it is prob'ly the chopper transistor on the input of the transformer or possibly the bridge recto.

We rarely bothered to repair them when I was a bench tech, (time is money...cheaper to replace than repair) so I ended up with a pile of them with various problems that I eventually repaired.